The turbine section of a gas turbine houses stages of turbine wheels, and is typically sealed such that all of the hot exhaust gas produced by the gas turbine passes through the turbine sections to generate power, and preferably all of the hot exhaust gas exits the gas turbine through an exhaust section. A gas turbine can be used in a cogeneration system by being coupled to a heat recovery generator that uses heat from the hot exhaust gas to produce steam.
Typically, the steam generated through the cogeneration operation is proportional to the power generation by the gas turbine. The exhaust gas produced by the gas turbine would be the sole contributor of heat in the heat recovery steam generator to produce steam. The quantity of hot exhaust gas produced by the turbine typically determines the amount of steam produced by recovering heat from the hot exhaust.
Occasions may arise when the demand for steam is greater than the demand for the amount of steam conventionally generated from the hot exhaust of the gas turbine. For example, during the winter time, it may be desirable to produce and provide more steam than power to the users. Conventionally, to produce an increase in steam, an increase of gas turbine exhaust production would be needed, and an increase in power from the gas turbine would also be generated proportionally. The extra power generated from the gas turbine may not be needed. Furthermore, more fuel to the gas turbine would be needed to produce more power and steam in the process. Thus, the cost of fuel and cost of operation may increase while producing a product that may not be desired in the output.